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    <meta charset="UTF-8">
    <meta name="viewport"
          content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
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    <title>Document</title>
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<script>
    /* todo
            js的函数 ， 形参和实参的个数可以不相同，但是实参必须大于等于形参，否则会报错；
     */
    let test01 = (a, b, c, d = 4) => {
        console.log(a , b , c , d);
    }
    test01(1, 2, 3);
    test01(1, 2);
    test01(1, 2, 3, 5 , 6);
    let test02 = (a, b) => {
        console.log(a , b);
    }
    test02(1, 2);
    test02(1);
</script>
</body>
</html>